Quantitative comparison of slope and river sediment dynamics in response to an upland extreme flood event

该项目的目的是对2008年10月23日至25日发生在英格兰北部北方湖区Coledale山谷的极端高地洪水进行定量评估。这一事件在该地区的大部分地区造成了广泛的破坏，并引起了全国的关注，当时极端的天气条件促使对极端的地方和区域洪水作出全面的紧急反应;山坡和河道普遍受到侵蚀。高地和山区极端事件期间的侵蚀在短期内占主导地位，并为长期景观发展提供条件。然而，人们对这些事件知之甚少，特别是对斜坡和河道对侵蚀的相对贡献。这一点很重要，因为未来的气候变化情景表明，高强度风暴事件的频率会增加，这可能会重新激活许多高地工业化景观中典型的旧污染沉积物储存。因此，对极端事件期间的侵蚀进行量化至关重要，以便在短期内进行有效的灾害管理，并制定长期的空间目标管理战略。在记录洪水事件时，需要作出紧急反应，以便洪水的关键证据不会因为随后的降雨侵蚀滑坡疤痕和碎片沉积物而丢失;洪泛区高水位线（残骸线）和沉积物迅速被植被掩盖或被清理作业扰乱。捕获“新鲜”证据意味着可以直接对过程进行编目，而不是在以后进行推断。该项目分为三个阶段：密集的实地工作;数据汇编和管理;地理信息系统分析/沉积物预算建设。这将使我们能够（1）清楚地建立在高地集水区的沉积物通量的联系和路径;（2）确定裸露和植被的斜坡在贡献沉积物的高地河道的相对重要性;和（3）评估存储在控制沉积物的下游通量的意义。该项目将建立在以前资助的NERC研究在同一流域通过使用现有的数据来源和科学的理解，以评估这一事件的意义。这包括对2005年1月的一次类似大洪水进行独特的流域地貌基线调查，其中已经包括一个描述流域地形、土壤、地貌和植被的地理信息系统和一个广泛的土壤特性数据库（岩土特性、体积密度等）。2005年和2008年在同一流域发生的两次非常大的高地洪水允许在同一流域的洪水之间进行直接比较，包括沉积物动力学和景观中与洪水相关的地貌特征的持续性。特别是，我们可以识别有用的特征，区分不同年龄的滑坡疤痕，在时间上紧密聚集。建立“最佳实践”，从一个单一的洪水识别证据是非常重要的极端事件的分析和统计依赖于“基本上完整的”清单的侵蚀功能从单一的事件。

The aim of this project is to make a quantitative assessment of slope and river sediment dynamics in response to an extreme upland flood which occurred in the Coledale Valley in the Lake District, Northern England on 23-25th October 2008. This event caused widespread disruption over much of the region, and captured national attention when extreme weather conditions prompted a full scale emergency response to extreme local and regional flooding; and widespread erosion of hillslopes and river channels. Erosion during extreme events in upland and mountain regions dominates erosion over the short-term and conditions longer term landscape development. However, little is known about these events and in particular, the relative contribution of slopes and river channels to erosion. This is important because future climate change scenarios suggest an increased frequency of high intensity storm events which can remobilise old contaminated sediment stores typical of many upland industrialised landscapes. Quantifying erosion during extreme events is therefore crucial so that effective hazard management can be undertaken in the short term and long-term spatially targeted management strategies devised. When documenting flood events an urgent response is required so that key evidence of the flood is not lost as subsequent rainfall erodes landslide scars and debris deposits; and floodplain high water marks (wrack lines) and sediments are rapidly masked by vegetation or disturbed by clean up operations. Capturing 'fresh' evidence means that processes can be catalogued directly and not inferred at a later date. The project is split into three phases: intensive fieldwork; data compilation and management; and GIS analysis/sediment budget construction. This will enable us to (1) clearly establish linkages and pathways of sediment flux in upland catchments; (2) determine the relative importance of bare and vegetated slopes in contributing sediment to upland river channels; and (3) evaluate the significance of storage in controlling the downstream flux of sediment. The project will build on previously funded NERC research in the same catchment by using existing data sources and scientific understanding to evaluate the significance of this event. This includes a unique catchment geomorphic baseline survey, of a similar large flood from January 2005, which already includes a GIS describing the topography, soil, geomorphology and vegetation of the catchment and an extensive data base of soil properties (geotechnical properties, bulk density, etc.). The occurrence of two very large upland floods in 2005 and 2008 in the same catchment allows direct comparison between the floods in the same valley in terms of sediment dynamics and the persistence of flood related geomorphic features in the landscape. In particular we can identify useful characteristics for differentiating landslide scars of differing age which are closely clustered in time. Establishing 'best practice' for identifying evidence from a single flood is very important for extreme event analysis and statistics which rely on 'substantially complete' inventories of erosion features from single events.